Transdermal delivery of pharmaceutical agents has proven effective for drugs that are able to move across the skin barrier. For example, small amounts of nicotine can be delivered over extended periods with transdermal patches that suspend the nicotine in an ethylene vinyl acetate (EVA) copolymer. See, e.g., Nicoderm-CQ® by GlaxoSmithKline (Brentford, UK). However, it is not possible to actively control the rate of administration. Rather, a series of different concentrations of nicotine suspended in EVA are provided to a user with instructions to use different patches on different days depending upon the treatment program or the level of craving.
It is recognized that the constant dosage delivered by a passive matrix of active agents may not be optimal for treating all conditions, however. For example, with respect to smoking cessation, it is recognized that the average smoker has cyclical cravings corresponding with normal daily activity, such as a waking, meals, etc. Accordingly, for some patients it is better to use a “dual therapy” including a transdermal patch and a fast acting delivery method, such as nicotine gum. See, Ebbert et al., Drugs 2010, 70(6), 643-650. Such dosing helps to wean the body from the dependency while also being responsive to the cyclical peak cravings. Other transdermally-delivered actives, such as insulin, also require “boosters” to overcome daily metabolic swings, e.g., following meals.
New “smart” transdermal patches that provide some ability to control dosing in real time, are currently being evaluated. For instance, Chrono Therapeutics (Hayward, Calif.) is currently testing a micropump-enabled smart transdermal patch for delivering nicotine. Chrono's device includes a “crave” button that allows users to receive a “booster” when cravings strike. Nonetheless, the Chrono device is larger than a typical transdermal patch and, thus, is visible through clothing as a sizeable bump. It also requires replacement cartridges and charging to maintain function. It is clear that there remains a need for a simple (and inexpensive) delivery system that provides for real-time modification of dosing.